I'm not making this pretty, here's a bunch of listings that all echo my assertions jumbled together. No time for pretty
All I'm saying with this info is that this is how I was taught when I was implementing LiIon charging circuits. Could this all be wrong? Maybe. But it's how I was taught and I'm still a believer in it.
ElectronicDesign
Perhaps one of the worst locations for a Li-ion battery is in a laptop computer when used daily on a desktop with the charger connected. Laptops typically run warm or even hot, raising the battery temperature, and the charger is maintaining the battery near 100% charge. Both of these conditions shorten battery life, which could be as short as six months to a year. If possible, the user should be instructed to remove the battery and use the ac adapter for powering the laptop when used as a desktop computer. A properly cared for laptop battery can have a service life of two to four years or more.
Using partial-discharge cycles can greatly increase cycle life, and charging to less than 100% capacity can increase battery life even further.
Use partial-discharge cycles
Using only 20% or 30% of the battery capacity before recharging will extend cycle life considerably. As a general rule, 5 to 10 shallow discharge cycles are equal to one full discharge cycle. Although partial-discharge cycles can number in the thousands, keeping the battery in a fully charged state also shortens battery life. Full discharge cycles (down to 2.5 V or 3 V, depending on chemistry) should be avoided if possible.
Avoid charging to 100% capacity
Selecting a lower float voltage can do this. Reducing the float voltage will increase cycle life and service life at the expense of reduced battery capacity. A 100-mV to 300-mV drop in float voltage can increase cycle life from two to five times or more. Li-ion cobalt chemistries are more sensitive to a higher float voltage than other chemistries. Li-ion phosphate cells typically have a lower float voltage than the more common Li-ion batteries.
From the Microsoft Document called "Caring for your surface battery"
Review tips on caring for your Surface battery. Maximize the health and lifespan of the battery in your Surface device to get the most from it.
support.microsoft.com
When using your device, make sure the battery drains below 50 percent regularly. This will help minimize aging of the battery cells.
Keeping or storing at a high state of charge: Batteries maintained at a high charge state will lose capacity faster. You can help prevent this accelerated process by not leaving your device connected to AC power for extended periods. Rather, try to ensure the device is regularly discharged below 50% before charging again. If you have a scenario where you need to keep the device plugged in continuously, we recommend using the Battery Limit Mode to limit the battery state of charge. If you need to store your device for a long period of time, it’s best to reduce the charge level to 50% before storing and to regularly check the battery to ensure it has not drained to very low levels.
Battery Limit Mode - Battery Limit Mode is a feature available for users who need to keep devices plugged in for extended periods of time. Plugging in the device for extended periods of time can cause batteries to prematurely age. When enabled this feature limits battery charging capacity to 50%, which slows the aging process and prolongs battery longevity.
From the Journal of Energy Storage: Strategies to limit degradation and maximize Li-ion battery service lifetime - Critical review and guidance for stakeholders
See the graphical abstract and asociated text.
From battery manufacturers:
EEMB (eemb.com)
Long-term Storage
The cell should be used within a short period after charging because long-term storage may cause
loss of capacity by self-discharging. If the cell is kept for a long time(3months or more), It is strongly
recommended that the cell isstored at dry and low-temperature and Keep the cell(s) at a half-charged
state. the cell should be shipped in 50% charged state. In this case, OCV is from 3.65V to 3.85V. Our
shipping voltage is 3.75-3.80v . because storage at higher voltage may cause loss of characteristics.
- over a period of 1 month: -5 ~ 35℃, relative humidity: ≤75%. - over a period of 6 months:
-20~ 25℃, relative humidity: ≤75%.
Battery data sheets often speficy that best storage practices dictate stoargae at levels well below 100% as this increases longevity of the batteries. Here is but a single example:
From the Panasonic Lithium Ion Batteries Technical Handbook:
Storing the Batteries
The batteries should be stored at room temperature, charged to about 30 to 50% of capacity.
We recommend that batteries be charged about once per year to prevent overdischarge.
Other sources:
DigitalTrends: You shouldn’t leave your laptop in this state all the time, though, just when you’d drain the battery very quickly. As mentioned, it’s better to store your battery at 40% to 50% capacity than it is to store it at 100% capacity if you don’t plan on using it for a bit. Degradation is faster on fully charged, unattended batteries, especially at high temperatures.
Tesla: Tesla recommends that if you are planning a long trip that requires near 100% charge that you set the timer to result in a full charge finishing within 60 minutes of departure. The idea here is to be fully topped off for as short an amount of time as possible.
Aceleron: For those of you who are battery fanatics and want to know the science behind charging your battery, here are some technical details:
For a lithium battery the structure of the positive terminal is variable when it is depleted of electrons for long periods of time, which can lead to permanent capacity loss. However, lithium’s low self-discharge rate means, that it does not need to be stored at 100% state of charge (SoC). In fact, a lithium battery should be stored near 50% state of charge – which equally distributes the electrons on the positive and negative terminals.
Or more simply, lithium battery chemistry is a bit like a hydro dam’s reservoir. In an ideal world, it would be best to keep the reservoir half full. An empty reservoir, and you have no power; but an overfilled dam can cause issues that damage the dam (overflow etc).
I know that you didn't trust the study from Battery University (although this was in fact an in depth study), but it might be worth noting that the following article from Steve Burke of Gamers Nexus also cites this as a source:
After our Gaming Laptop Buyer's Guide, it seemed fitting to follow-up with a post that explains how to take care of Lithium-Ion laptop batteries and make them last longer. -
www.gamersnexus.net
See the text of the article for more info.
